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pt::peg::to::cparam(3tcl) Parser Tools pt::peg::to::cparam(3tcl) 





NAME


pt::peg::to::cparam - PEG Conversion. Write CPARAM format






SYNOPSIS


package require Tcl 8.5


package require pt::peg::to::cparam ?1.1.2?


pt::peg::to::cparam reset


pt::peg::to::cparam configure


pt::peg::to::cparam configure option


pt::peg::to::cparam configure option
    value...


pt::peg::to::cparam convert serial










DESCRIPTION


Are you lost ? Do you have trouble understanding this document ?
    In that case please read the overview provided by the Introduction to
    Parser Tools. This document is the entrypoint to the whole system the
    current package is a part of.


This package implements the converter from parsing expression
    grammars to CPARAM markup.


It resides in the Export section of the Core Layer of Parser
    Tools, and can be used either directly with the other packages of this
    layer, or indirectly through the export manager provided by
    pt::peg::export. The latter is intented for use in untrusted
    environments and done through the corresponding export plugin
    pt::peg::export::cparam sitting between converter and export
  manager.


IMAGE: arch_core_eplugins






API


The API provided by this package satisfies the specification of
    the Converter API found in the Parser Tools Export API
  specification.



  

  
This command resets the configuration of the package to its default
      settings.

  

  
This command returns a dictionary containing the current configuration of
      the package.

  

  
This command returns the current value of the specified configuration
      option of the package. For the set of legal options, please read
      the section Options.

  

  
This command sets the given configuration options of the package,
      to the specified values. For the set of legal options, please read
      the section Options.

  

  
This command takes the canonical serialization of a parsing expression
      grammar, as specified in section PEG serialization format, and
      contained in serial, and generates CPARAM markup encoding the
      grammar, per the current package configuration. The created string is then
      returned as the result of the command.








OPTIONS


The converter to C code recognizes the following configuration
    variables and changes its behaviour as they specify.



  

  
The value of this option is the name of the file or other entity from
      which the grammar came, for which the command is run. The default value is
      unknown.

  

  
The value of this option is the name of the grammar we are processing. The
      default value is a_pe_grammar.

  

  
The value of this option is the name of the user for which the command is
      run. The default value is unknown.

  

  
The value of this option is a string into which to put the generated text
      and the other configuration settings. The various locations for user-data
      are expected to be specified with the placeholders listed below. The
      default value is "@code@".







  
@user@

  
To be replaced with the value of the option -user.

  
@format@

  
To be replaced with the the constant C/PARAM.

  
@file@

  
To be replaced with the value of the option -file.

  
@name@

  
To be replaced with the value of the option -name.

  
@code@

  
To be replaced with the generated Tcl code.







  

  
The following options are special, in that they will occur within the
      generated code, and are replaced there as well.







  
@statedecl@

  
To be replaced with the value of the option state-decl.

  
@stateref@

  
To be replaced with the value of the option state-ref.

  
@strings@

  
To be replaced with the value of the option string-varname.

  
@self@

  
To be replaced with the value of the option self-command.

  
@def@

  
To be replaced with the value of the option fun-qualifier.

  
@ns@

  
To be replaced with the value of the option namespace.

  
@main@

  
To be replaced with the value of the option main.

  
@prelude@

  
To be replaced with the value of the option prelude.







  

  
A C string representing the argument declaration to use in the generated
      parsing functions to refer to the parsing state. In essence type and
      argument name. The default value is the string RDE_PARAM p.

  

  
A C string representing the argument named used in the generated parsing
      functions to refer to the parsing state. The default value is the string
      p.

  

  
A C string representing the reference needed to call the generated parser
      function (methods ...) from another parser fonction, per the chosen
      framework (template). The default value is the empty string.

  

  
A C string containing the attributes to give to the generated functions
      (methods ...), per the chosen framework (template). The default value is
      static.

  

  
The name of the C namespace the parser functions (methods, ...) shall
      reside in, or a general prefix to add to the function names. The default
      value is the empty string.

  

  
The name of the main function (method, ...) to be called by the chosen
      framework (template) to start parsing input. The default value is
      __main.

  

  
The name of the variable used for the table of strings used by the
      generated parser, i.e. error messages, symbol names, etc. The default
      value is p_string.

  

  
A snippet of code to be inserted at the head of each generated parsing
      function. The default value is the empty string.

  

  
The number of characters to indent each line of the generated code by. The
      default value is 0.

  

  
A flag controlling the generation of code comments containing the original
      parsing expression a parsing function is for. The default value is
      on.




While the high parameterizability of this converter, as shown by
    the multitude of options it supports, is an advantage to the advanced user,
    allowing her to customize the output of the converter as needed, a novice
    user will likely not see the forest for the trees.


To help these latter users an adjunct package is provided,
    containing a canned configuration which will generate immediately useful
    full parsers. It is



  

  
Generated parsers are embedded into a Critcl-based framework.








C/PARAM CODE REPRESENTATION OF PARSING EXPRESSION GRAMMARS


The c format is executable code, a parser for the grammar.
    The parser implementation is written in C and can be tweaked to the users'
    needs through a multitude of options.


The critcl format, for example, is implemented as a canned
    configuration of these options on top of the generator for c.


The bulk of such a framework has to be specified through the
    option -template. The additional options



  

  

  

  

  

  

  

  

  

  

  

  

  

  

  

  




provide code snippets which help to glue framework and generated
    code together. Their placeholders are in the generated code. Further
    the options



  

  

  

  




allow for the customization of the code indent (default none), and
    whether to generate comments showing the parsing expressions a function is
    for (default on).




EXAMPLE


We are forgoing an example of this representation, with apologies.
    It would be way to large for this document.








PEG SERIALIZATION FORMAT


Here we specify the format used by the Parser Tools to serialize
    Parsing Expression Grammars as immutable values for transport, comparison,
    etc.


We distinguish between regular and canonical
    serializations. While a PEG may have more than one regular serialization
    only exactly one of them will be canonical.



  

  







  
[1]

  
The serialization of any PEG is a nested Tcl dictionary.

  
[2]

  
This dictionary holds a single key, pt::grammar::peg, and its
      value. This value holds the contents of the grammar.

  
[3]

  
The contents of the grammar are a Tcl dictionary holding the set of
      nonterminal symbols and the starting expression. The relevant keys and
      their values are







  

  
The value is a Tcl dictionary whose keys are the names of the nonterminal
      symbols known to the grammar.







  
[1]

  
Each nonterminal symbol may occur only once.

  
[2]

  
The empty string is not a legal nonterminal symbol.

  
[3]

  
The value for each symbol is a Tcl dictionary itself. The relevant keys
      and their values in this dictionary are







  

  
The value is the serialization of the parsing expression describing the
      symbols sentennial structure, as specified in the section PE
      serialization format.

  

  
The value can be one of three values specifying how a parser should handle
      the semantic value produced by the symbol.







  

  
The semantic value of the nonterminal symbol is an abstract syntax tree
      consisting of a single node node for the nonterminal itself, which has the
      ASTs of the symbol's right hand side as its children.

  

  
The semantic value of the nonterminal symbol is an abstract syntax tree
      consisting of a single node node for the nonterminal, without any
      children. Any ASTs generated by the symbol's right hand side are
      discarded.

  

  
The nonterminal has no semantic value. Any ASTs generated by the symbol's
      right hand side are discarded (as well).











  

  
The value is the serialization of the start parsing expression of the
      grammar, as specified in the section PE serialization format.







  
[4]

  
The terminal symbols of the grammar are specified implicitly as the set of
      all terminal symbols used in the start expression and on the RHS of the
      grammar rules.







  

  
The canonical serialization of a grammar has the format as specified in
      the previous item, and then additionally satisfies the constraints below,
      which make it unique among all the possible serializations of this
      grammar.







  
[1]

  
The keys found in all the nested Tcl dictionaries are sorted in ascending
      dictionary order, as generated by Tcl's builtin command lsort
      -increasing -dict.

  
[2]

  
The string representation of the value is the canonical representation of
      a Tcl dictionary. I.e. it does not contain superfluous whitespace.








EXAMPLE


Assuming the following PEG for simple mathematical expressions






PEG calculator (Expression)


    Digit      <- '0'/'1'/'2'/'3'/'4'/'5'/'6'/'7'/'8'/'9'       ;


    Sign       <- '-' / '+'                                     ;


    Number     <- Sign? Digit+                                  ;


    Expression <- Term (AddOp Term)*                            ;


    MulOp      <- '*' / '/'                                     ;


    Term       <- Factor (MulOp Factor)*                        ;


    AddOp      <- '+'/'-'                                       ;


    Factor     <- '(' Expression ')' / Number                   ;
END;





then its canonical serialization (except for whitespace) is






pt::grammar::peg {


    rules {


        AddOp      {is {/ {t -} {t +}}                                                                mode value}


        Digit      {is {/ {t 0} {t 1} {t 2} {t 3} {t 4} {t 5} {t 6} {t 7} {t 8} {t 9}}                mode value}


        Expression {is {x {n Term} {* {x {n AddOp} {n Term}}}}                                        mode value}


        Factor     {is {/ {x {t (} {n Expression} {t )}} {n Number}}                                  mode value}


        MulOp      {is {/ {t *} {t /}}                                                                mode value}


        Number     {is {x {? {n Sign}} {+ {n Digit}}}                                                 mode value}


        Sign       {is {/ {t -} {t +}}                                                                mode value}


        Term       {is {x {n Factor} {* {x {n MulOp} {n Factor}}}}                                    mode value}


    }


    start {n Expression}
}











PE SERIALIZATION FORMAT


Here we specify the format used by the Parser Tools to serialize
    Parsing Expressions as immutable values for transport, comparison, etc.


We distinguish between regular and canonical
    serializations. While a parsing expression may have more than one regular
    serialization only exactly one of them will be canonical.



  

  







  

  







  
[1]

  
The string epsilon is an atomic parsing expression. It matches the
      empty string.

  
[2]

  
The string dot is an atomic parsing expression. It matches any
      character.

  
[3]

  
The string alnum is an atomic parsing expression. It matches any
      Unicode alphabet or digit character. This is a custom extension of PEs
      based on Tcl's builtin command string is.

  
[4]

  
The string alpha is an atomic parsing expression. It matches any
      Unicode alphabet character. This is a custom extension of PEs based on
      Tcl's builtin command string is.

  
[5]

  
The string ascii is an atomic parsing expression. It matches any
      Unicode character below U0080. This is a custom extension of PEs based on
      Tcl's builtin command string is.

  
[6]

  
The string control is an atomic parsing expression. It matches any
      Unicode control character. This is a custom extension of PEs based on
      Tcl's builtin command string is.

  
[7]

  
The string digit is an atomic parsing expression. It matches any
      Unicode digit character. Note that this includes characters outside of the
      [0..9] range. This is a custom extension of PEs based on Tcl's builtin
      command string is.

  
[8]

  
The string graph is an atomic parsing expression. It matches any
      Unicode printing character, except for space. This is a custom extension
      of PEs based on Tcl's builtin command string is.

  
[9]

  
The string lower is an atomic parsing expression. It matches any
      Unicode lower-case alphabet character. This is a custom extension of PEs
      based on Tcl's builtin command string is.

  
[10]

  
The string print is an atomic parsing expression. It matches any
      Unicode printing character, including space. This is a custom extension of
      PEs based on Tcl's builtin command string is.

  
[11]

  
The string punct is an atomic parsing expression. It matches any
      Unicode punctuation character. This is a custom extension of PEs based on
      Tcl's builtin command string is.

  
[12]

  
The string space is an atomic parsing expression. It matches any
      Unicode space character. This is a custom extension of PEs based on Tcl's
      builtin command string is.

  
[13]

  
The string upper is an atomic parsing expression. It matches any
      Unicode upper-case alphabet character. This is a custom extension of PEs
      based on Tcl's builtin command string is.

  
[14]

  
The string wordchar is an atomic parsing expression. It matches any
      Unicode word character. This is any alphanumeric character (see alnum),
      and any connector punctuation characters (e.g. underscore). This is a
      custom extension of PEs based on Tcl's builtin command string
    is.

  
[15]

  
The string xdigit is an atomic parsing expression. It matches any
      hexadecimal digit character. This is a custom extension of PEs based on
      Tcl's builtin command string is.

  
[16]

  
The string ddigit is an atomic parsing expression. It matches any
      decimal digit character. This is a custom extension of PEs based on Tcl's
      builtin command regexp.

  
[17]

  
The expression [list t x] is an atomic parsing expression. It
      matches the terminal string x.

  
[18]

  
The expression [list n A] is an atomic parsing expression. It
      matches the nonterminal A.







  

  







  
[1]

  
For parsing expressions e1, e2, ... the result of [list /
      e1 e2 ... ] is a parsing expression as well. This is the
      ordered choice, aka prioritized choice.

  
[2]

  
For parsing expressions e1, e2, ... the result of [list x
      e1 e2 ... ] is a parsing expression as well. This is the
      sequence.

  
[3]

  
For a parsing expression e the result of [list * e] is a
      parsing expression as well. This is the kleene closure, describing
      zero or more repetitions.

  
[4]

  
For a parsing expression e the result of [list + e] is a
      parsing expression as well. This is the positive kleene closure,
      describing one or more repetitions.

  
[5]

  
For a parsing expression e the result of [list & e] is a
      parsing expression as well. This is the and lookahead
    predicate.

  
[6]

  
For a parsing expression e the result of [list ! e] is a
      parsing expression as well. This is the not lookahead
    predicate.

  
[7]

  
For a parsing expression e the result of [list ? e] is a
      parsing expression as well. This is the optional input.









  

  
The canonical serialization of a parsing expression has the format as
      specified in the previous item, and then additionally satisfies the
      constraints below, which make it unique among all the possible
      serializations of this parsing expression.







  
[1]

  
The string representation of the value is the canonical representation of
      a pure Tcl list. I.e. it does not contain superfluous whitespace.

  
[2]

  
Terminals are not encoded as ranges (where start and end of the
      range are identical).








EXAMPLE


Assuming the parsing expression shown on the right-hand side of
    the rule








    Expression <- Term (AddOp Term)*





then its canonical serialization (except for whitespace) is








    {x {n Term} {* {x {n AddOp} {n Term}}}}











BUGS, IDEAS, FEEDBACK


This document, and the package it describes, will undoubtedly
    contain bugs and other problems. Please report such in the category
    pt of the Tcllib Trackers
    [http://core.tcl.tk/tcllib/reportlist]. Please also report any ideas for
    enhancements you may have for either package and/or documentation.


When proposing code changes, please provide unified diffs,
    i.e the output of diff -u.


Note further that attachments are strongly preferred over
    inlined patches. Attachments can be made by going to the Edit form of
    the ticket immediately after its creation, and then using the left-most
    button in the secondary navigation bar.






KEYWORDS


CPARAM, EBNF, LL(k), PEG, TDPL, context-free languages,
    conversion, expression, format conversion, grammar, matching, parser,
    parsing expression, parsing expression grammar, push down automaton,
    recursive descent, serialization, state, top-down parsing languages,
    transducer






CATEGORY


Parsing and Grammars






COPYRIGHT


Copyright (c) 2009 Andreas Kupries <andreas_kupries@users.sourceforge.net>








  

    1.1.2
    tcllib